High temperature resistant door seal for a microwave oven

ABSTRACT

A microwave energy door seal includes a choke seal and a high temperature resistant dissipative seal, with the dissipative seal being located adjacent the door passage for the choke seal. Further a second dissipative type seal is located on the door spaced from the high temperature resistant dissipative type seal. The high temperature resistant seal comprises a ferrite ensleeved in a glass fiber braid mounted to the door or opposite oven frame with spring means for holding it in place as well as biasing the ensleeved ferrite into abutting contact with an oven member surface.

United States Patent 1191 Valles Nov. 5, 1974 [5 HIGH'TEMPERATURERESISTANT DOOR 3,678,238 7/1972 Yasuoka m1. 219/1055 SEAL FOR AMICROWAVE OVEN 3,679,855 7/1972 Binzer 219/1055 3,812,316 5/1974 Milburn219/1055 [75] Inventor: Benjamin Vera Valles, San Jose,

m OTHER PUBLICATIONS T. Moreno, "Microwave Transmission Design Data",[73] Assignee. Systems, Inc., San Carlos, Reprinted 195 p g I 69 [22]Filed: 1974 Primary Examiner-J. V. Truhe 21 APPL 441,044 AssistantExaminer-Hugh D. Jaeger Attorney, Agent, or Firm-Ronald M. Goldman [52]US. Cl 219/1055, 49/479, 87/6,

174/35 0c, 219/397, 277/230 1 [571 ABSTRACT [51] Int. Cl. 1105b 9/06 Amicrowave energy door seal includes a choke seal [58] Field of Search174/35 CC, 356 MS; and a high temperature resistant dissipative seal,with 277/230, 234, 235 R, 235 A; 219/1055, 396, the dissipative sealbeing located adjacent the door 397, 413; 29/193; 49/479; 87/6 passagefor the choke seal. Further a second dissipative type seal is located onthe door spaced from the [56] References Cited high temperatureresistant dissipative type seal. The UNITED STATES PATENTS hightemperature resistant seal comprises a ferrite en- 2 956 143 10/1960Scha 219/10 55 sleeved in a glass fiber braid mounted to the door or2:958:754 11/1960 Hahn .1111:IIIIIIIIIIII: 219/1055 "P1395ite Oven framewith Spring means for hOIdlng it 3,182,164 5/1965 ll'ollfleld 219/1055in Place as Well as biasing the ensleeved ferrite into 3,196,242 7/1965De Vries et al 219/1055 ti g Contact i an oven member Surface- 3,413,40611 1968 Plummer 174/35 GC 3,502,784 311970 Kunkel 174/35 oc 23 Clams 8Draw F'gures FER'RITE GLASS 6/F1BER FER|R|TE GLASS /FIBER Q 25 I 26 Fig-7 A l 1 i K I l l .040 .060 .080 .IOO .020 .l40 .I6O .l80

SPACING BETWEEN DOOR 8| OVEN FLANGE (INCHES) PATENIEDHUV 5 I914 3.846508sum aer 3 HIGH TEMPERATURE RESISTANT DOOR SEAL FOR A MICROWAVE OVENBACKGROUND OF THE INVENTION Certain enclosures require seals to preventhigh frequency radiation, such as microwave frequency energy, fromleaking through physical gaps between a movable enclosure door whichcloses the entrance of the enclosure and the enclosure frame. Thisrequirement for effective microwave energy door seals is mostpredominant in the microwave oven, a cooking appliance in whichfoodstuffs are cooked or heated by exposure to microwave energy.Typically the microwave oven includes a metal walled container orenclosure which in turn contains a metal walled cooking chamber, anannular frame portion at the front surrounding the cooking chamber whichextends between the chamber and, for example, the outer wall of theenclosure, and a movable door which in its closed position covers theentrance to the cooking chamber as well as a major portion or all of theannulus. For this purpose various types of microwave energy seals havebeen employed either separately or in combination, in order to meet therigid requirement that microwave leakage between the door and ovenchamber be on the order of 1.0 milliwatt or less, measured at a distanceof 5 centimeters from any portion of the oven door, when the oven is inoperation. Familiar types of door seals include what is referred to asthe choke seal, contact seal, and dissipative seal. The choke seal isbased upon the analogy to a short-circuited microwave transmission lineor choke stub, as variously termed, of a length equal to one-halfwavelength at the operating frequency. The dissipative seal relies uponthe principle of absorbing and dissipating incident microwave energyradiation, and a contact seal relies on the principle of providing ametal barrier, a tight metal-to'metal contact between the door and frameto eliminate any gaps between the movable door and the enclosure throughwhich leakage might occur. Various past door seal designs includecombinations of one or more of these individual door seals based on thepremises that two seals perform better than a single seal, three sealsperform better than two seals, etc., until at some point the additionalcost of an additional seal exceeds the expected improvement indecreasing leakage.

As an example, in U.S. Pat. No. 3,196,242 to De- Vries, graphitematerial, a microwave absorptive material, is distributed about theperiphery of the oven door as a seal to dissipate microwave frequencyleakage. lronfield, U.S. Pat. No. 3,182,164, shows and teaches variousembodiments of a choke seal," and Schall, U.S. Pat. No. 2,956,]43,discloses a metal-to-metal contact seal and a lossy rubber seal. And asis found in Moreno, Microwave Transmission Design Data, DoverPublications, reprinted 1958, page 169, the combination of a choke sealand a lossy rubber seal spaced therefrom is disclosed as a means ofpreventing microwave energy leakages between waveguide joints. Althoughthese seals serve theirpurposes satisfactorily, further developments incooking appliances dictate that the microwave oven be combined with aconventional electric oven that includes pyrolytic cleaning deviceswhich are found in the conventional types of self-cleaning electricranges. As is known, pyrolytic oven cleaning devices operateon theprinciple of heating the oven to a very high temperature so as tocompletely vaporize any grease or other dirt on the oven walls.Obviously vaporization conveniently eliminates the need for manual orchemical removal of greases and stains from the oven chamber walls. Thehigh temperatures at which the pyrolytic cleaning devices operate imposenew requirements on door seals: the door seal must prevent leakage ofmicrowave energy and withstand high temperatures. Thus the loss loadedconductive rubber seal if exposed to such high temperatures willdecompose. And various other types of lossy materials must be evaluatedto determine whether they are physically damaged or whether they maylose their microwave energy absorptive characteristics if heated tothose high temperatures.

OBJECTS OF THE INVENTION Accordingly it is an object of my invention toprovide an improved microwave energy door seal for a microwave oven thatis not subject to damage through exposure to very high temperatures.

It is another object of my invention to provide an improved microwaveoven door seal which is capable of withstanding the high oventemperatures characteristic of pyrolytic cleaning devices.

It is an additional object of my invention to provide a door seal thatprovides unusually good results in minimal leakage.

And it is a still further object of my invention to provide aconstruction for a dissipative seal which is simple to construct,assemble, and install.

' tion includes a choke seal, characterized by a first conductivelybounded chamber having a passage in the door annulus with such passagespaced a predetermined distance from the oven chamber, a dissipativeseal characterized by an open chamber adjoining the chamber of the chokeseal and bounded by a metal wall common to the first chamber spacing thetwo chambers by approximately one-one sixtieth wavelength (0.03- inch)and a ferrite element protruding from said opening in said chamber withunderlying spring means within said second chamber for urging saidferrite member into abutment with the oven frame.

In accordance with another aspect of my invention the ferrite member andthe spring are enclosed in a single glass fiber sleeve and the sleeve isdivided into two compartments, suitably by a seam. The glass fibersleeve is pervious to microwave energy, introduces a gap between theferrite and the oven frame, and is thermally insulative to serve as aheat block.

The invention is further characterized by a second dissipative seal,characterized by a carbon loaded rubber gasket, which forms a surroundon the inner annulus of the door located more proximate the outerperiphery of the door than the aforementioned seals.

The foregoing and other objects and advantages of my invention as wellas the elements characteristic of my invention, including equivalentsand substitutions therefor, are better understood by givingconsideration to the detailed description of the various embodiments ofthe invention, which follows, taken together with the illustrativefigures of the drawings.

In the drawings:

FIG. 1 illustrates an external view of the'improved door seal of myinvention;

FIG. 2 illustrates in partial section one embodiment of my invention;

FIG. 3-illustrates in partial section another embodiment of myinvention;

FIG. 4 illustrates an exploded view of some door elements which appearin the section of FIG. 3; FIG. 5 illustrates a novel construction of adissipative type door seal of my invention;

DETAILED DESCRIPTION -A microwave oven 1 is illustrated in perspectivein FIG. 1. The oven includes a cavity 3, which is bordered at the frontby a frame or annulus 5, and a control panel 7, and an oven door 9,shown ajar.

The inner surface of oven door 9 is visible in FIG. 1 and permits a viewof-some external portions of the door seals formed within the doorproper, which is hereinafter explained and disclosed in greater detail.The door is supported to the oven frame by two hinges, l1 and 13, whichare of a conventional structure and allows the door to swing out to thefully opened position illustrated. Although I illustrate a swing-outtype of door support, it is understood that the operation of the doorseals hereinafter described are independent of the particular way in'which the oven door is attached to the oven and that the invention isequally applicable to oven doors which are hingedly mounted to a sidewall and open outwardly to the right or to the left. Likewise as isknown to those skilled in the art. any one or more of the described doorseals may be installed or formed in the annulus or frame portion 5 andin which the door surface is employed as an electrically conductive sur'face.

Conventionally oven 1 forms an enclosure or container which houses allthe conventional elements of the microwave oven, including the powersupply and microwave energy source, not illustrated. Typically themicrowave source generates a frequency of 2,450 MHz. The oven contains acooking chamber or cavity 3 which is open at the front, in which thefoodstuffs to be cooked are set in place. Typically the oven cavity is ametal walled inner container having dimensions greater thanone-wavelength at the operating frequency of the enclosed microwavesource. The cavity has, suitably, a porcelainized or vitreous enamelsurface finish. Suitable openings into this chamber, not visible in thefigure, such as the opening for admitting microwave energy, the Cal-rodbrowning elements installed on the upper chamber wall, and the pyrolyticself-cleaning elements, are enclosed in the chamber but are not visiblein the figure nor are they necessary to an understanding of theinvention. The frame portion or annulus 5 extends between oven cavityand the outer oven walls. A portion of the annulus 5,, is elevated. Thecontrol panel portion 7 which contains the numerous switches, timercontrol knobs, etc., conventional in the microwave oven, appears on theright side in the figure for purposes of perspective completeness onlysince the details thereof are not necessary to the understanding of theinvention and are not further described.

The microwave oven illustrated to place my invention in its context isthe familiar countertop or portable variety. It is understood, however,that the invention is utilized in and forms part of the conventionalbuilt-in type ovens in which the microwave oven is built into aconventional electric range, the latter of which is more likely tocontain pyrolytic self-cleaning elements. The important relevantphysical element is the annulus 5 and the oven chamber 3 since it isthese elements which cooperate with the door mounted elements to formthe door seal.

Door 9 is constructed of various parts including an outer panel 15 andan inner panel 17. As illustrated in the figure, the inner panel 17 hasa protruding portion which protrudes into the oven cavity 3 slightlywhen the door is in the closed position. Although I illustrate theprotrusion to be constructed of metal, it is also within the scope ofthe invention to install in this protruding portion a glass windowsuitably protected with a nonradiating metal grill of any conventionaland known structure.

A flange edge 19 and the second flange edge 21 border an opening 23which forms the passage to a first chamber or cavity, not visible inthis figure, which functions as a choke type of seal, hereinafterillustrated and explained in greater detail. Another opening exitsbetween flange edge 21 and another flanged edge 25 and a protrudingbraided glass fiber strip 27 is located in that opening. As ishereinafter brought out in greater detail, the glass fiber stripencloses a ferrite material and protrudes from another chamber, notillustrated in this figure, in which the braided material is situated.This ferrite material functions as a seal. Finally, a resilient carbonloaded rubber strip 29 extends around the inner annulus of the door mostadjacent the outer periphery of the door to form a gasket-like seal.

The various structural elements comprising the door seal extend entirelyaround the periphery of the door inner annulus exposing to view whatappears to be a series of concentric rectangles of a picture-frame"shaped geometry and each of these elements is located in the annularinner door portion aligned so as to overlie annulus 5 of the oven frameproper when the door is in the closed position.

The foregoing explains the arrangement and the ex- I ternal features ofthe elements of the door seals visible on the outside surfaces of theinner surface of the door together with the relationship thereof to theabutting or underlying annulus 5 of the oven. A better understanding ofthe structures forming the seals is obtained by considering partialsections of doors such as is found in the details of two differentstructures hereinafter presented in FIG. 2 and in FIG. 3.

It is noted in connection with the description of the figures which arehereinafter described, the numerical designation of the elementsemployed are the same numbers used to refer to those same elements foundand described in connection with the description of FIG. I. The doorconstruction in FIG. 2 utilizes a solid piece of material, forillustrative purposes, such as cast aluminum, and has the outer panel 15attached. The annulus of the oven frame 5 as well as the chamber wall ofoven cavity 3 and the outer wall of the oven are annulus which overliesthe most adjacent side wall of oven chamber 3. Of course, this grooveextends completely around the door panel in a rectangular pictureframegeometry, as was described and visible in FIG. 1. At the frequency of2,450 MHz one wavelength is ap' proximately 4.8 inches in length. Astrip of glass fiber material, 26, is installed in the upper end of thepassage 23 to function as a dirt seal. The glass fiber material ispervious to microwave frequency energy but forms a barrier to particlesof dirt and grease.

The second chamber, 28, is similarly fashioned by a deep groove in thedoor whichextends around the door in a picture-framelike geometry. Thesecond chamber shares a common narrow wall 20 terminating in flange edge21 with the first chamber. Suitably the edge 21 is no more than one-onesixtieth wavelength in width so as to space the two chambers as closelytogether as is possible by less than one-twentieth wavelength (0.240inches). Other choices within a desired range for this spacing may be0.02 inches to 0.20 inches, 0.02 inches to 0.24 inches, and 0.025 inchesto 0.05 inches. The second chamber also encloses a spring, 30, at thebottom end and a rectangular ferrite strip 32. Spring 30 is suitably atubular braided spring such as is available from the Bentley-HarrisCompany and this exerts a radially outward force. In turn, the springand ferrite strip are ensleeved in the braided glass fiber sheath 27.The door hinge 11, partially illustrated, is shown attached to the innerside 17 of door 9.

When the door 9 is in the closed position the rubber seal is compressedbetween the door frame and door to provide a tight seal. Spring 30forces the ensheathed ferrite 32 into abutment with the door frameannulus 5. It is noted that the glass fiber braid 27 slightly spaces andprevents ferrite 32 from actual contact with the door frame annulus.

Inasmuch as the glass fiber is pervious to microwave energy andessentially nondissipative, it is equivalent to a slight gap between thedoor and frame. Likewise if the door annulus is covered by aporcelainized coating that in itself is equivalent to a further physicalgap.

As is evident to one skilled in the art, a solid door made of castaluminum is very expensive and is, in a sense, impractical. At best itis useful to illustrate the elements of the invention without thecomplications of flanges and other structural assemblies hereinafterintroduced to the reader. Thus a more practical embodiment of theinvention is illustrated in the partial section of the door illustratedin FIG. 3. The door in this practical embodiment includes a plurality ofinterconnected panels and is internally hollow. The outer panel and theinner door panel 17 are interconnected through a support bracket, suchas main door member 31. Door member 31 is joined to panel 15, suitablyby screws, such as screws 33. Door member 31 is also joined to innerpanel 17 by a mounting hat or bracket 35, the latter of which isattached to main door member 31 suitably by a screw 37, and to innerpanel 17 together with an intermediate flange 39 sandwiched therebetweenby a weld. Metal flange 39 is of a picture-framelike rectangularstructure and includes an upwardly projecting lip 20 which terminates inedge 21, and a second upwardly projecting lip 38 which is in contactwith panel 17. In cross section, bracket 39 resembles a channel and partof this channel is covered by a portion of inner panel 17.

It is noted that the edge 19 of inner panel 17 is spaced from edge 21 toform a passage 23, and the bracket 39 together with the overlyingportion of panel 17 forms a metal walled chamber cavity which functionsas a choke" type seal. Suitably this cavity is approximately one-fourthwavelength in length and one-twentieth wavelength wide. The passage 23is located approximately one-fourth wavelength from the adjacent wall 40of cooking cavity 3 so that the total distance to the short-circuited(metal walled) end 38 of the chamber is about one-half wavelength. Astrip of braided glass fiber 26 is conveniently inserted into and issituated in the chamber physically filling or plugging" the entrance tothis chamber and forms a dirt seal. A rectangular picture-framelikemetal bracket or channel assembly 41 having a U-shaped cross section isattached to the underside of bracket 39, as shown at one stem of the U,suitably by spot welds, so that the base of the .U is a slight distancefrom lip 20 of bracket 39. Another bracket 43, of a picture-framelikegeometry, having an L-shaped cross section, is joined to bracket 41 nearan end of the base stem of the L, suitably by screws, such as screw 45,as illustrated, and with the other stem of the L extending up to theplane of door panel 17. The

upper edge 25 of the L-shaped bracket is spaced from the edge 21 ofbracket 39 to similarly define a passage and the inner sides of bracket45, the base of bracket 41, and bracket 39 define a second chamber whichextends about the door annulus which shares in common at least one wallportion 20, terminating in edge 21, with that of the first chamber. Thesecond chamber includes an enlarged portion on the bottom end. Anelongated braid spring 30 is installed in the enlarged portion of thischamber and a ferrite dissipative material 32 is installed in the frontend of the chamber substantially plugging or filling the chamberentrance. Both the spring and the ferrite material are sheathed in abraided glass fiber sheath 27. The diameter of spring 30 is larger thanthe passage formed between edges 21 and 25 of the bracket sides. Thusduring assembly the spring is radially compressed and pushed into itsposition in the chamber whence the spring restores to its full diameter.Thus this seal assembly is retained in place in the door and can beremoved only by exerting a sufficient pulling force on the sheath. Stillanother rectangular bracket 51, having an L-shaped cross section, issupported by main door member 31 by means of various L-shaped brackets,53, joined to member 31 by screws 55 and 57. The rubber gasket strip 29is a graphite loaded rubber material. It is shaped so as to have ahook-like underlying portion. This hook-like portion is inserted withinthe space 62 and grips bracket 31 to hold the rubber seal in place onthe door.

To illustrate this practical construction of the elements and thisgeometrical relationsip more closely, I provide the exploded view ofFIG. 4. In FIG. 4 four of panel 17, the metal bracket 39, the supportbracket 41 and bracket 43. Each of the elements is of a rectangularpicture-frame geometry and are of appropriate dimension so as to fittogether to form the chambers and passages within the door as observedin cross section in FIG. 3.

The construction details of the ferrite dissipative seal assembly isillustrated in FIG. 5. As is there shown, the

braided glass fiber sheath 27 is divided into two elongate compartmentsby a seam 28. The lowermost compartment'contains the elongated wire meshspring 30, which is exposed in the figure for clarity of illustration.The upper compartment contains the ferrite 32 which is also exposed inthis illustration. The ferrite 32 is an elongated rectangular strip. Aplurality of these ferrite strips are inserted end to end into thesecond compartment. Obviously only a portion of the seal is illustratedand a length sufficient to extend around the annulus portion of the dooris used. The ferrite material withstands the high temperatures to whichit is exposed in the oven, and the glass fiber braided strip is anexcellentthermal insulator, and hence in the combination in the oven itserves the additional purpose of providing a thermal seal or "heatblock."

In operation the oven chamber is exposed to microwave frequencyradiation, typically of a frequency of 2,450 megahertz. As is known, thechoke seal is designed anddimensioned as an analogy to a waveguidetransmission line, and as is known the input electrical impedancecharacteristic of a one-half wavelength short-circuited waveguidetransmission line to microwave. frequency fields at that frequency isideally zero ohms, or in other words a short-circuit. Hence ideally theinput electrical impedance to the physical gap between the door and ovenis very very low so as to effectively shunt or bridge the field currentsacross the physical gap. Since the input physical gap extends all aroundthe inner periphery of the door it may be more accurate to analogize toa series of such transmission lines connected together. However oneskilled in the art views the choke seal, it is expectedly not perfectand does allow some leakage current to flow. This leakage is incidentupon the dissipative seal ferrite 32. The dissipative seal converts theincident microwave energy to heat as a characteristic of the materialmuch as is done by the foodstuffs being cooked in the oven chamber.Since there is only a minute amount of leakage energy there is only aminute amount of heat generated in the first dissipative seal. Inasmuchas the fiberglass sheath 27 enclosing the ferrite 32 is pervious tomicrowave energy, there is provided a further path for microwave energyto pass if it is not fully dissipated in seal 32. The third seal 29 ismade of graphite loaded pliant rubber and is hence a dissipative type ofdoor seal.

With the door closed the rubber is somewhat compressed between the doorand oven frame and eliminates any gaps. Ideally any microwave energywhich leaks past the first dissipative seal is absorbed in this seconddissipative seal. However as is hereinafter described in connection withthe discussion of the results of one practical embodiment of theinvention, some minute permissible level of leakage does occur and ismeasurable.

FIG. 6 illustrates a simplified symbolic drawing of the cross-section ofpart of the door and door seal of the invention, and FIG. 6,, similarlyillustrates a similar but not identical door and door seal whichdoes-not incorporate the invention. Thus FIG. 6,, shows the oven door 9,the choke seal chamber having anentrance 26', a second chamber 50containing the spring 30 and the protruding ferrite 32'. The loss loadedrubber seal 29' is attached to the inner annulus of the door near thedoors outer periphery. The first chamber and second chamber 30 have thewall SI in common, and the width of that wall is less than approximatelyonetwentieth wavelength. For purposes of this illustration the glassfiber sheath enclosing the spring and the ferrite are omitted. As isevident, this cartoon schematic is representative of the details of thestructure illustrated in both FIG. 2 and FIG. 3. The structurerepresented in FIG. 6,, likewise illustrates the door 9", a choke sealchamber having an entrance 26", a second chamber 50" housing a spring30" and protruding ferrite 32". The loss loaded rubber perimeter seal29'. is attached to the inner annulus of the door. The first and secondchambers do not have a common wall, but are separated by an edge 52"which is greater than onetwentieth wavelength in length.

The difference between FIG. 6,, and FIG. 6,, is that in FIG. 6,, the twochambers have a thin wall 51' in common, which spaces the chambers by adistance of only one-fiftieth wavelength or less, whereas in theschematic of FIG. 6,, the two chambers are separated a greater distanceby an annulus portion of the door 52'.

Reference is now made to FIG. 7 which illustrates graphically theradiation in units of milliwatts measured at a distance of 5 centimetersfrom the door to oven boundary as a function of the gap spacing betweenthe door seals on the movable door and the annulus or frame of the ovencontainer in an oven operating to provide 2,450 MHz microwave energy inthe cooking chamber. These measurements were accomplished on a doorconstructed in accordance with the teachings of FIG. 3 and representedby schematic FIG. 6,, with the distance between the chambers, i.e., thethickness of 0 wall 21" being 0.030 inches, to obtain the results inCurve A, and with the door modified to conform to the schematicillustration of FIG. 6,,, where the ferrite seal was moved an additionalthree-eighths inch away from the first chamber, to obtain the results ofCurve B. To form the physical gaps various thicknesses of nonconductiveor substantially nondissipative material, such as mylar, is insertedbetween the door and the annulus of the oven container. Such materialwas a plurality of A inch thick square spacers to cover only a portionof the door perimeter. Curve C is a straight line and repre sentsradiation of one milliwatt per square centimeter measured at a distanceof 5 centimeters, which is the maximum radiation permitted by currentUS. Government regulations. As is apparent from Curve A, the level ofthe leakage radiation for all gap spacings is substantially lower thanthe maximum permitted by Government standard. As is also apparent fromCurve B, in the case of the door seal in which the ferrite dissipativeseal is spaced a greater distance from the choke seal, the leakageradiation is substantially higher initially and exceeds the Governmentstandard for a great number of gap spacings. In practice the doorconfiguration represented by the schematic of FIG. 6,, is substantiallybetter than any door seal arrangement known to applicant. Curve Dillustrates the results when a 3 inch X 4 inch paper pad, of variousthicknesses, simulating an entrapped hot pad, was inserted between thedoor and the oven across the door annulus including the dissipativeseals, without allowing microwave energy leakage above the Governmentstandard. This indeed was unexpected to me and is in my opinionsignificant. From a technical standpoint, I did not perceive that thearrangement of the three seals or their juxtaposition provided thesynergistic effect which apparently has been demonstrated by theresults. I can only speculate that the narrow edge of the common metalwall separating the choke and ferrite seals concentrates any leakagefields in the ferrite material where it is better absorbed as a possiblereason for such unexpected and substantially improved results. Inaddition to having a microwave door seal that meets present Governmentstandards and withstands pyrolytic oven temperatures, the present sealin my opinion advances the art in that even very large gaps, such asone-eighth inch, do not produce energy leakage that I regard assignificant, being below the Government limit as shown in Curves A andD. As is known, ovens shipped from the factory must conform to theleakage standards set by the Government. On the other hand, if the ovenis not maintained properly in use, certain increases in leakagenecessarily result. Instructions in present oven clearly specified thatthe user should clean the annulus of the oven and door to prevent thebuild-up of dirt and grease, which due to their accumulation can resultin a gap between the door and the oven container, and microwave energyin amounts above the desired standard would leak. With a rather largepublic there are always a number of persons whose personal habits maypreclude the implementation of such instructions and-who choose toassume the risk of disregarding warnings.

With the present invention it is apparent that substantial amounts ofgrease build-up, dirt or other material can accumulate between the doorand the oven chamber, and even so, only acceptable levels of leakageoccurs. In effect, the door seal of the invention provides suchsignificant results that it can even protect those additional personsagainst their own improvidence and lack of good judgment in failing tofollow instructions and warnings in the care and use of the microwaveoven.

It is clear from the foregoing construction and mode of operation of thedoor seals that the function of the door seal is independent of whetherits structure is supported by or formed within the movable door, such asdoor 9 in FIG. 1, or is instead supported by or formed in the annulussurrounding the entrance to the oven chamber in FIG. 1. Clearly inaccordance with the teachings of my invention and as is known in theprior art, suitable seals may be mounted or formed in the annulus 5region and the inner annular door portion may instead be a solidconductive metal surface. Likewise, any one of the seals may be mountedon the oven chamber annulus and the remaining ones of the door sealsmounted on the inner annular door portion. This is simply a reversal ofparts between different portions of the closure members consisting ofthe door and the frame. It is clear that my invention is intended tocover the door seal arrangements as described in the appended claims,irrespective of their position, i.e., door or frame support, and it isdesired that my claims be so construed to include this equivalent.

It is believed that the preceding description of the preferredembodiments of my invention disclose my invention in sufficient detailto enable one skilled in the art to make and use my invention. Howeverit is expressly understood that my invention is not to be limited tothose particular details inasmuch as various modifications, additionsand equivalents suggest themselves to one skilled in the art uponreading this specification.

Accordingly my invention is to be broadly construed within the fullspirit and scope of the appended claims.

What I claim is:

I. In a microwave oven having a heating chamber within which foodstuffsto be heated by exposure to microwave energy radiation are received, anentry opening at an end of said chamber to provide access to saidchamber, an annular border region surrounding said entry opening, and amovable door operable between an open and closed position to preventexit of microwave energy radiation, said door including a middle doorportion to cover said entry opening to said chamber and an annularborder region about said middle door portion which covers, at least inpart, said annular border region surrounding said heating chamber entryopening to form opposed annular regions, and microwave energy seal meansto prevent radiation leakage from physical gaps between said annulardoor portion and annular border region; the improvement in saidcombination wherein said microwave energy seal means comprises:

a choke type seal which includes a first elongated continuouselectrically conductive walled cavity of predetermined depth locatedbehind one of said annular border regions and extending about said entryopening; and

' a narrow opening in said first cavity located in said one of saidannular border regions and extending entirely about said entry openingand spaced a predetermined distance from said entry opening forproviding microwave energy pervious path between said cavity and fromabout said opposed annular regions;

a dissipative seal which includes a second elongated cavity underlyingone of said annular regions and extending about said entry opening, anarrow opening in said second cavity located in said one of said annularregions and extending about said entry opening and spaced apredetermined distance therefrom for providing a passage between saidannular region and said second cavity,

microwave energy dissipating means located partially within, extendingabout, and protruding from said narrow opening in said second cavity,

spring means located within and extending about said second cavity forproviding a force on said dissipative means in a direction outwardly ofsaid second cavity to force said dissipative means outwardly from saidopening in said second cavity and apply a pressure to the opposed one ofsaid annular regions;

a third seal which includes a compressible strip of electrically lossymaterial located on one of said annular regions and extending about saidentry opening for compressive engagement between said annular doorregion and said annular border region surrounding said chamber; and

wherein said opening in said first cavity is spaced from said opening insaid second cavity by a prede- 1 l termined distance within the range of0.02 and 0.24 inch and is located more proximate said entry opening thansaid opening in said second cavity and wherein said opening in saidsecond cavity is located more proximate said entry opening than saidthird seal.

2. The invention as defined in claim 1 wherein said dissipative sealfurther comprises an elongated sleeve of high temperature resistantpliant microwave energy pervious material, said sleeve being dividedinto two elongated compartments and wherein each of said mi-, crowaveenergy dissipating means and said spring means are located within saidsleeve.

3. The invention as defined in claim 2 wherein said microwavedissipative material comprises a ferrite.

4. The invention as defined in claim 3 wherein said spring comprises awire mesh tubular spring.

5. The invention as defined in claim 2 wherein said sleeve materialcomprises braided glass fiber fibers.

6. The invention as defined in claim 4 wherein said wire mesh tubularspring has a predetermined crosssectional diameter and wherein saidpredetermined diameter is greater than the width of said narrow openingin said second cavity.

7. The invention as defined in claim 1 wherein said predetermineddistance between said opening in said first cavity and said opening insaid second cavity comprises approximately 0.03 inch.

8. The invention as defined in claim 6 wherein said predetermineddistance between said opening in said first cavity and said opening insaid second cavity comprises between 0.025 inch and approximately 0.050inch.

9. The invention as defined in claim 1 wherein said one of said annularregions, which said second elongated cavity underlies, comprises saidannular border region on said door.

10. The invention as defined in claim 9 wherein said one of said annularborder regions in which said first cavity is located behind, comprisessaid annular border region of said door. I

11. The invention as defined in claim 10 wherein said one of saidannular region on which said third seal is located, comprises saidannular border region of said door.

12. The invention as defined in claim 6 wherein said one of said annularregions, which said second elongated cavity underlies, comprises saidannular border region on said door.

13. The invention as defined in claim 12 wherein said one of saidannular border regions in which said first cavity is located behind,comprises said annular border region of said door.

14. The invention as defined in claim 13 wherein said one of saidannular region on which said third seal is located, comprises saidannular border region of said door.

15. The invention as defined in claim 6 further comprising a dirt seal,said dirt seal comprising a high temperature resistant material perviousto microwave frequency energy and relatively impervious to dirtparticles, said dirt seal located in said opening in said first cavity.

16. The invention as defined in claim 15 wherein said compressiblestripof electrically lossy material comprises a rubber having asubstantially lower temperature resistance than said sleeve and saidferrite.

17. The invention in a dissipative seal which comprises:

a door for a microwave oven;

a cavity in said door extending thereabout in a continuous loop;

a narrow opening in the surface of said door, said opening extendingabout said door in said same continuous loop;

an elongated sleeve of braided glass fiber material, said sleeve beingdivided into two elongated compartments and extending about said cavity;

an elongated tubular mesh spring installed m one of said compartmentsand ferrite material installed in the other of said compartments, andwherein the diameter of said tubular mesh spring is greater than thewidth of said opening, said tubular mesh spring being located withinsaid cavity and said ferrite material and a portion of said sleeveprotruding from said opening.

18. In a microwave oven having a cooking chamber for receivingfoodstuffs to be heated, outer walls forming a container within whichsaid oven chamber is located and a front wall portion between said outerwalls and said cooking chamber to form an annular region about saidcooking chamber, and a movable door for closing the front end of saidchamber, said door having an annular region which overlaps said annularregion of said container when said door is in the closed position, theimprovement therein comprising:

a first conductively walled chamber located within said door, saidchamber having a passage opening in said annular region and spaced apredetermined distance from said cooking chamber for providing amicrowave energy leakage-inhibiting effect;

a second chamber, said second chamber having a restricted portion and anopening therein in said annular portion of said door, said secondchamber having a metal wall in common with said first chamber, said wallhaving an edge exposed in said annular portion, said wall having athickness in the range of 0.02 to 0.20 inch;

microwave energy absorbing material located in said second chamber andprotruding therefrom for abutment with said annular container portionand spring means located in said chamber for biasing said microwaveenergy absorbing material against movement into said chamber; and

a loss-loaded rubber strip formin a gasket between said annular portionsof said oor and said container.

19. The invention as defined in claim 18 wherein each of said annularportions of said door and said oven corlitainer include a coating ofvitreous enamel materia Y 20. The invention as defined in claim 19further comprising a sleeve of high temperature resistant pliantmaterial and wherein each of said spring means and said microwave energyabsorbing means are positioned within said sleeve.

21. The invention as defined in claim 20 further comprising seam meansfor dividing said sleeve into two compartments and wherein saidmicrowave energyabsorbing material is located in a first compartment andsaid spring means is located in a second compartment.

22. The invention as defined in claim 21 wherein said sleeve materialcomprises braided glass fiber.

23. The invention as defined in claim 22 further comprising a strip ofglass fiber material positioned within said entrance of said firstcavity for providing a barrier to dirt particles while permittingpassage of microwave energy therebetween.

1. In a microwave oven having a heating chamber within which foodstuffsto be heated by exposure to microwave energy radiation are received, anentry opening at an end of said chamber to provide access to saidchamber, an annular border region surrounding said entry opening, and amovable door operable between an open and closed position to preventexit of microwave energy radiation, said door including a middle doorportion to cover said entry opening to said chamber and an annularborder region about said middle door portion which covers, at least inpart, said annular border region surrounding said heating chamber entryopening to form opposed annular regions, and microwave energy seal meansto prevent radiation leakage from physical gaps between said annulardoor portion and annular border region; the improvement in saidcombination wherein said microwave energy seal means comprises: a choketype seal which includes a first elongated continuous electricallyconductive walled cavity of predetermined depth located behind one ofsaid annular border regions and extending about said entry opening; anda narrow opening in said first cavity located in said one of saidannular border regions and extending entirely about said entry openingand spaced a predetermined distance from said entry opening forproviding microwave energy pervious path between said cavity and fromabout said opposed annular regions; a dissipative seal which includes asecond elongated cavity underlying one of said annular regions andextending about said entry opening, a narrow opening in said secondcavity located in said one of said annular regions and extending aboutsaid entry opening and spaced a predetermined distance therefrom forproviding a passage between said annular region and said second cavity,microwave energy dissipating means located partially within, extendingabout, and protruding from said narrow opening in said second cavity,spring means located within and extending about said second cavity forproviding a force on said dissipative means in a direction outwardly ofsaid second cavity to force said dissipative means outwardly from saidopening in said second cavity and apply a pressure to the opposed one ofsaid annular regions; a third seal which includes a compressible stripof electrically lossy material located on one of said annular regionsand extending about said entry opening for compressive engagementbetween said annular door region and said annular border regionsurrounding said chamber; and wherein said opening in said first cavityis spaced from said opening in said second cavity by a predetermineddistance within the range of 0.02 and 0.24 inch and is located moreproximate said entry opening than said opening in said second cavity andwherein said opening in said second cavity is located more proximatesaid entry opening than said third seal.
 2. The invention as defined inclaim 1 wherein said dissipative seal further comprises an elongatedsleeve of high temperature resistant pliant microwave energy perviousmaterial, said sleeve being divided into two elongated compartments andwherein each of said microwave energy dissipating means and said springmeans are located within said sleeve.
 3. The invention as defined inclaim 2 wherein said microwave dissipative material comprises a ferrite.4. The invention as defined in claim 3 wherein said spring comprises awire mesh tubular spring.
 5. The invention as defined in claim 2 whereinsaid sleeve material comprises braided glass fiber fibers.
 6. Theinvention as defined in claim 4 wherein said wire mesh tubular springhas a predetermined cross-sectional diameter and wherein saidpredetermined diameter is greater than the width of said narrow openingin said second cavity.
 7. The invention as defined in claim 1 whereinsaid predetermined distance between said opening in said first cavityand said opening in said second cavity comprises approximately 0.03inch.
 8. The invention as defined in claim 6 wherein said predetermineddistance between said opening in said first cavity and said opening insaid second cavity comprises between 0.025 inch and approximately 0.050inch.
 9. The invention as defined in claim 1 wherein said one of saidannular regions, which said second elongated cavity underlies, comprisessaid annular border region on said door.
 10. The invention as defined inclaim 9 wherein said one of said annular border regions in which saidfirst cavity is located behind, comprises said annular border region ofsaid door.
 11. The invention as defined in claim 10 wherein said one ofsaid annular region on which said third seal is located, comprises saidannular border region of said door.
 12. The invention as defined inclaim 6 wherein said one of said annular regions, which said secondelongated cavity underlies, comprises said annular border region on saiddoor.
 13. The invention as defined in claim 12 wherein said one of saidannular border regions in which said first cavity is located behind,comprises said annular border region of said door.
 14. The invention asdefined in claim 13 wherein said one of said annular region on whichsaid third seal is located, comprises said annular border region of saiddoor.
 15. The invention as defined in claim 6 further comprising a dirtseal, said dirt seal comprising a high temperature resistant materialpervious to microwave frequency energy and relatively impervious to dirtparticles, said dirt seal located in said opening in said first cavity.16. The invention as defined in claim 15 wherein said compressible stripof electrically lossy material comprises a rubber having a substantiallylower temperature resistance than said sleeve and said ferrite.
 17. Theinvention in a dissipative seal which comprises: a door for a microwaveoven; a cavity in said door extending thereabout in a continuous loop; anarrow opening in the surface of said door, said opening extending aboutsaid door in said same continuous loop; an elongated sleeve of braidedglass fiber material, said sleeve being divided into two elongatedcompartments and extending about said cavity; an elongated tubular meshspring installed in one of said compartments and ferrite materialinstalled in the other of said compartments, and wherein the diameter ofsaid tubular mesh spring is greater than the width of said opening, saidtubular mesh spring being located within said cavity and said ferritematerial and a portion of said sleeve protruding from said opening. 18.In a microwave oven having a cooking chamber for receiving foodstuffs tobe heated, outer walls forming a container within which said ovenchamber is located and a front wall portion between said outer walls andsaid cooking chamber to form an annular region about said cookingchamber, and a movable door for closing the front end of said chamber,said door having an annular region which overlaps said annular region ofsaid container when said door is in the closed position, the improvementtherein comprising: a first conductively walled chamber located withinsaid door, said chamber having a passage opening in said annular regionand spaced a predetermined distance from said cooking chamber forproviding a microwave energy leakage-inhibiting effect; a secondchamber, said second chamber having a restricted portion and an openingtherein in said annular portion of said door, said second chamber havinga metal wall in common with said first chamber, said wall having an edgeexposed in said annular portion, said wall having a thickness in therange of 0.02 to 0.20 inch; microwave energy absorbing material locatedin said second chamber and protruding therefrom for abutment with saidannular container portion and spring means located in said chamber forbiasing said microwave energy absorbing material against movement intosaid chamber; and a loss-loaded rubber strip forming a gasket betweensaid annular portions of said door and said container.
 19. The inventionas defined in claim 18 wherein each of said annular portions of saiddoor and said oven container include a coating of vitreous enamelmaterial.
 20. The invention as defined in claim 19 further comprising asleeve of high temperature resistant pliant material and wherein each ofsaid spring means and said microwave energy absorbing means arepositioned within said sleeve.
 21. The invention as defined in claim 20further comprising seam means for dividing said sleeve into twocompartments and wherein said microwave energy-absorbing material islocated in a first compartment and said spring means is located in asecond compartment.
 22. The invention as defined in claim 21 whereinsaid sleeve material comprises braided glass fiber.
 23. The invention asdefined in claim 22 further comprising a strip of glass fiber materialpositioned within said entrance of said first cavity for providing abarrier to dirt particles while permitting passage of microwave energytherebetween.